As a '70's era Head, I avoided this show for numerous reasons. (Yes, Jerry's voice is what it is. But Jerry would not have the eloquence and the emotional impact that he does on KNOCKIN' ON HEAVEN'S DOOR if he were not.)
There is so much here to appreciate that does not depend on Jerry's voice. (You have permission to skip those songs.) I am not a fan of Hall & Oats, but listen to the whole band on WHAT'S GOIN' ON and you'll find Jerry speaking to us through his other instrument.
Brininging in guest vocalists at this point would not have been a bad idea. (Listen to Lowell George's vocals on GOOD LOVIN' from the SHAKE DOWN STREET OUTTAKES and you get a sense of the possibilities.)